PROJECT SUMMARY/ABSTRACT Approximately 3% percent of infants and children 6 to <72 months have strabismus or amblyopia. The development of amblyopia and strabismus are proposed to be the result of abnormal visual experience. Normal visual experience depends on both good retinal image quality and eye alignment, which require complex interactions between the afferent and efferent visual systems. Understanding these interactions are critical to both the development of preventive measures and the accumulation of evidence-based treatment strategies for strabismus and amblyopia. Hyperopic infants who do not emmetropize are at risk for developing strabismus and amblyopia with as little as 2D spherical equivalent (SE), and that risk increases exponentially with every added diopter of uncorrected hyperopia. Moreover, the infants who are less likely to emmetropize, are the ones who do not accommodate well to a near stimulus. Specific Aim 1: To test the hypothesis that there is a deficit in or immaturity of the afferent visual system that causes poor blur detection which subsequently results in a decreased efferent accommodative response. We will examine retinal blur detection in infants with typical refractive error and with moderate/high hyperopia longitudinally at 3- and 9-months of age. Specific Aim 2: To test the hypothesis that the tonic adaptive components of accommodation are the primary factors responsible for the manifestation of accommodative esotropia in young children with clinically significant hyperopia. We will measure the phasic response and tonic adaptive components of the adult oculomotor control model in children ages 2 to <6 years with moderate/high hyperopia, including some with accommodative esotropia prior to refractive error correction. Long term Goal: Provide pediatric vision care practitioners with the ability to identify: [a] which infants with hyperopia will emmetropize and which will not and [b] of the infants who do not emmetropize, which ones will go on to develop strabismus and amblyopia. Improved ability to identify infants at highest risk will lead to improved patient outcomes.